Such a cable is required to have a high tensile strength and to be able to fully withstand its winding up and its drawing out by a capstan because it is towed by a vessel, wound up on the vessel or pulled in the sea.
Such a conventional cable comprises a cable core transferring a signal or electric power, a lapping tape and an inner sheath on the cable core, a tension member provided on the inner sheath, an interposing member provided on the tension member to control the specific gravity of the cable, and an outer sheath provided on the interposing member with another lapping tape disposed between the interposing member and the outer sheath.
Since the undersea high strength cable has a long length of more than 1,000 m, the cable is stressed by an extremely high tensile force when it is pulled in the sea or wound up. Therefore, the tension member is so designed to fully withstand such a high tensile force. When the cable is wound up on the vessel by a capstan, for example, the drawing force from the capstan is at first applied to the outer sheath, and then transferred to the tension member provided inside the outer sheath. However, in the prior art undersea high strength cable constructed in accordance with the above description, since the interposing member between the outer sheath and the tension member is provided to control the specific gravity, the integrity of the outer sheath with the tension member is incomplete. Thus, it will be found that a high tensile force applied to the outer sheath causes a slight elongation of the outer sheath. This causes a displacement between the outer sheath and the tension member. As such a displacement is accumulated in a longitudinal direction, a portion of the outer sheath is deformed in a bellows manner, and as a result, if the cable is used as it is, the outer sheath will tend to be broken.